The laughs that pepper "Savannah Disputation" come with the regularity of a sitcom laugh track. Yet at its core, Evan Smith's recent comedy, now in a sly, entertaining production at the Old Globe, wrestles with the polarizing religiosity that pollutes the national dialogue.

And just as there's a stealth theme about tolerance and intellectual humility lurking beneath the laughs, the Globe production, buoyantly directed by Kim Rubinstein, also has a secret weapon ---- actor Nancy Robinette. Her performance is a vivid tour de force as Mary, the self-styled "born mean" sister who wants to "crush" a perky evangelical stalking her Roman Catholic household like an unwanted cat.

Mary and Margaret are almost-elderly sisters living together in Savannah, Ga., long settled into a life in which combative Mary fights with every shopkeeper over pennies and meek Margaret perpetually wears an apron to keep house. Every Thursday, she makes dinner for their parish priest.

The sisters' familiar pattern is shattered when Margaret (Mikel Sarah Lambert) opens the front door to admit the young blond proselytizer Melissa (Kimberly Parker Green). Her cheery manner disguises biblical absolutism. She views Catholicism as the Whore of Babylon and the sisters as misguided souls bound for eternal damnation. "Nice," she warns them, "doesn't get you into heaven."

Righteous Mary throws the girl out, but Margaret, timid in her faith and keenly aware of her mortality, is not so sure. Shaken, she invites the girl back. Predictably, Melissa's absurdly literal and rigid didacticism drives a wedge between the sisters.

"Your whole church is founded on a grammatical error," Green's smiling Melissa tells them, elucidating a favorite evangelical misreading of a Greek gospel.

Mary is soon comically reduced to defending the infallibility of the Pope's pronouncements by saying, "If you never hear it in the first place, you don't have to believe it!" She knows she's losing the argument, so, without telling him what she's up to, she brings in the big gun, her one pal at Blessed Sacrament Church, Father Murphy.

Robinette conveys Mary's scheming with such sadistic delight that the character sheds 10 years before the priest gets there. In contrast, Lambert's subtly panicked Margaret exudes innocence and expectation verging on terror. Conflict unnerves her. Twice it sends her fleeing to her room.

James Sutorius scores again at the Globe as Father Murphy, rounding out this expert cast of four. Dressed (by designer Judith Dolan) in nondescript sport clothes and a beige jacket, vaguely hunched and mild in his manners, Sutorius creates a self-erasing priest, as bland as the banana-pudding-with-vanilla wafers he eats when the living room disputation goes too far.

Why Mary saw this milquetoast as a militant defender of her faith remains a mystery until just before the end. Then, the playwright has Father Murphy switch gears so abruptly, he's almost unrecognizable. Once a theologian and scholar, he shows Melissa the error of her ways, yet he also makes surprisingly rigid demands of his own upon the newly heretical Mary. Hilariously, she has excommunicated herself because he's told her she must believe in the resurrection of the body, a tenet of her faith she finds ridiculous, and downright repulsive. Post-casket, where will she shower?

Not to put to fine a point upon the matter, for this is a boisterous mainstream comedy, but Smith does makes excellent use of that cornerstone of Catholic (also "Christian") doctrine about "the resurrection of the body." Whether by artistic design or poetic happenstance, the play's humor, debates and out-and-out fights unveil the characters' vulnerabilities, vis a vis their bodies, this side of the grave.

Sex has brought neither joy nor solace to any of them. The celibate priest takes comfort in being a eunuch by choice. Mary's rage comes partly from being dumped by her husband ---- and for a Baptist! Margaret is a spinster who seems to have missed her one chance with a loving mate. And the evangelical is a man-hunter, unlucky in love, and destined, perhaps, to return to the Lancome counter, not her missionary "vocation."

Very few available men have joined Melissa's denomination, the Evangelical Church of the Holy Spirit Alliance Church. Could religion be the opiate of the sexually unfulfilled?

As local audiences learned when Smith's rhyming satire of Victorian marriage ("The Uneasy Chair") was smartly produced at North Coast Repertory Theatre, this playwright knows how to write crackling dialogue, craft smart jokes and construct a scene and a play. "Savannah Disputation" contains no thematic breakthroughs or theatrical innovations. And though it may not have quite the same appeal for Buddhists, Jews or Muslims as for recovering Catholics like me, Rubinstein's excellent Globe production engages heart and mind through laughter, start to finish.

"The Savannah Disputation"

When: 8 p.m. Thursdays-Saturdays; 2 p.m. Saturdays and Sundays; 7 p.m. Sundays, Tuesdays and Wednesdays; through Nov. 1

Where: The Old Globe at the James S. Copley Auditorium, San Diego Museum of Art, Balboa Park, San Diego

Tickets: $29-$59

Info: 619-234-5623

Web: oldglobe.org